1. Field of the Invention
The present invention relates to a refrigerating unit having a refrigerating machine oil using polyol ester oil as its base oil in a refrigeration cycle using hydrofluorocarbon system refrigerants such as 1,1,1,2-tetrafluoroethane (hereunder to be called R134a).
2. Background Art
Compressors for a refrigerator and an automatic vending machine as well as a show case have used in many cases dichlorodifluoromethane (hereunder to be called R12) as a conventional refrigerant. This R12 has become the object of regulated fluorocarbons because of the problem of destruction of the ozone layer. And as the alternative refrigerant of this R12, the hydrofluorocarbon (HFC) refrigerant and the fluorocarbon (FC) refrigerant representing R134a are being studied as the refrigerants for a refrigerator, which is disclosed, for example, in the Japanese Patent Laid-Open Publication No. 1-271491.
However, there is a problem related to the lubrication of the compressor because the refrigerant R134a has a worse compatibility with such refrigerating machine oils such as mineral oil and alkylbenzene now being used and because of the aggravation of oil return to the compressor and also the suction of isolated refrigerant during its re-start when the refrigerating machine oil has separated from the refrigerant while the refrigerator was stopped.
For this reason, the inventors studied the polyol ester system oil as the refrigerating machine oils because it has compatibility with the refrigerant R134a. However, it is known that this polyol ester system oil causes erosion of the sliding members by the fatty acid produced after the decomposition of said oil and causes an abrasion if this oil is being used in a refrigerant compressor, especially to a rotary type compressor.
And as a result of studying many times in order to combine the R134a as a refrigerant with the polyol ester system oil as a refrigerating machine oil, the inventors have discovered that the polyol ester system oil causes hydrolysis by the influence of water with the rise of its total acid number, and a metallic soap is produced which becomes a sludge, giving an adverse influence on the refrigeration cycle, and that decomposition, oxidation deterioration and polymerization reactions are caused by the influences of oxygen and chlorine, and the metallic soap and the high molecule sludge are produced which exert an adverse influence on the refrigeration cycle.
The inventors have also found a problem in that the chlorine system refrigerant is also mixed into the hydrofluorocarbon refrigerant being sealed especially during the refrigeration cycle, and if the mixed volume should be large, the chlorine volume becomes large, which invites the generation of metallic soap and the generation of high molecule sludge by the decomposition, oxidation deterioration and polymerization reaction of polyol ester oil, and stays stagnant in the evaporator and the like of the refrigeration cycle.
In addition, the inventors have also learned that the problem as described above is also caused if the volume of chlorine should be large that remains behind in the component parts such as the compressor, condenser, various kinds of pipes, etc. which make up the refrigerating unit.
Moreover, the inventors have also ascertained that the generation of such a problem occurs when mineral oil has been conventionally used during the machining and assembling of component parts, and because this mineral oil can not be dissolved easily into the refrigerant of hydrofluorocarbon, it becomes solidified and stays stagnant in the evaporator and the like during the refrigeration cycle, aggravates the refrigeration capability and damages the equipment if said mineral oil should stay stagnant in excess of a certain level of volume.
Therefore, in the refrigerating unit using the polyol ester oil and the hydrofluorocarbon system refrigerant, the inventors have found out that the said problems can be solved by using a particular polyol ester oil, adding a special additive to said oil, maintaining the purity of hydrofluorocarbon system refrigerant at a high value and suppressing the equilibrium water content or chlorine residual volume of the refrigeration cycle. Moreover, the inventors have found out that the problematic point can be solved by installing a sludge catcher for capturing the sludge during the refrigeration cycle.
This invention is for solving the said problem and its object is to solve the said problem when the polyol ester system oil having the compatibility with the hydrofluorocarbon system refrigerant (for example, R134a) has been used as the refrigerating machine oil and to obtain a favorable refrigerating unit.